Centralized traffic controlling system



Sept. 17,1940. N. D. PREST ON CENTRALIZED TRAFFIC CONTROLLING SYSTEM 2 Sheets-Sheet 1 Filed March 3, 1932 i cow 8N T? N Q? Sept. 17, 1940; N, D. PRESTON CENTRALIZED TRAFFIC CONTROLLING SYSTEM Filed March 3, 1932 2 Sheets-Sheet 2 Patented Sept. 17, 1940 UNITED sfra'rss IGENTRAIIJZED TRAFFIC CONTROLLING SYSTEM Neil D.Preston, Rochester, N. Y., assignor to General Railway Signal Company, Rochester, N. Y.

Application March 3, 1932, Serial No. 596,516 25 Claims. (01; 177 -353) This invention relates to centralized trafiic control systems for railroads, and more particularly pertains to the communication part of such systems.

This application is a continuation in part of my prior application Ser No. 589,186 filed January 27, 1932, and the subject matter which is common between this application and said prior application is to be claimed in this application.

The present invention contemplates a centralized trafiic control system in which the switches 'and signals at a single station located along a railroad system are placed under the supervision of an operator at a central control ofiice; and in which the condition of such switches, signals and various other traffic conditionsat that location will be transmitted to the control office for providing the operator with the information necessary for the governing of train movements. In a system of this type, the switches and signals are associated with such automatic block signa1-' ling means as may be necessary under the particular circumstances met in practice in order that the manual control by the operator may be effected in a safe and reliable manner.

It often happens that there are several outlying track switches with their associated signals located adjacent or near each other, which traflic governing devices are preferably governed from a central tower of an interlocking plant or other ofiice already established. Ordinarily such control would be efiected over the usual direct'line wire type of system, but the present invention provides a selector type system particularly adapted to an installation of this type.

' The present invention more particularly relates to the communication part of such a centralized traific control system, and proposes to provide a communication system having only two line wires extending between the control office and the out- :lying field station. In this communication system, either control impulses are transmitted from the control ofiice, or indication impulses are transmitted from the field station duringany particular operating cycle; and these impulses 'are made distinctive by reason of their polarity for the purpose of transmitting the desired controls or indications. To accomplish this, the system of the present invention provides that a battery or other suitable source is located at each of the two locations, namely, at the control office and at the outlying field station, with the control apparatus and the circuits so arranged that irrespective of the smiultaneous occurrence of control and indication condtions, only one location or the other is effective to transmit impulses at anyone time. I

Irrespective of whether the control office or the outlying field station is effective to place distinctive impulses upon the line'circuit, the duration of these impulses is determined in the con-- trol o-ffice. Thus, the system of the present invention simplifies the timing characteristics of that type of communication system in which cutlying field stations are permitted totransmit impulses from their own local sources of energy.

These characteristic features of the present invention, thus briefly stated, will be explained more in detail in the following description of one embodiment of the invention; and various other characteristic features, functions and advantages of a system embodying this invention will be in part pointed out and in part apparent as the description progresses.

In describing the invention in detail, reference will be made to the accompanying drawings, in which similar parts throughout the several views are designated by similar reference characters, and in which:

Fig. 1 illustrates the apparatus and circuit arrangements provided for a typical control oifice arranged according to the present invention; and,

Fig. 2 illustrates the apparatus and circuit are rangements employed at a typical field station for indication impulses to and from that field station in accordance withthe present invention, and

adapted tobe associated with the apparatus employedin the control ofiice illustrated in Fig. 1.

Althoughthepresent invention has been shown applied to the control of a single switch and its associated signals, such as used at one end of a passing siding, it should be understood that the invention is not limited, as thus shown, to the control of only one switch and its signals, but may be extended for any desired number of switches and signals and may be readily applied to all types of track layouts. In the event, that a large number of switches and signals are located at the field station requiring the reception of controls and the transmission of indications, the system may be extended in any one of several ways. For example, a greater number of steps may be employed to thereby merely duplicate the apparatus illustrated. Another alternative would be to divide the controls and indications or detracting from the scope thereof.

For the purpose of simplifying the illustration and facilitating in the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed, the drawings having been made more for the purpose of making it easy to under- ,stand the principles and mode of operation, than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts are illustrated in a cone ventional manner, and symbols are used to indicate connections to the terminals of batteries,

101 other sources of electric current, instead of showing all the wiring connections to these terminals.

The symbols (-1-) and are employed to indicate the positive and negative terminals respectively of suitable potentials, or other sources of direct current; and the circuits with which these symbols are used-always have current fiowing in the same direction. The symbols (3+) and (B) indicate connections to the opposite terminals of a suitable battery, or other direct current source which has a central or intermediate tap designated (CN); and the circuits with which these symbols are used, may have current flowing in one direction or the other depending upon the particular terminal used in combination with the central or intermediate tap (CN) In general, the system includes a control office equipment interconnected with a field station equipment by two line wires, namely, a common line wire l0 and a control line wire 12. At the control. oflice a tower battery TB is provided with a center tap connected to the common wire ID; and similarly, at the field station a field battery FB is provided with a center tap connected to the common wire It. A polar line relay L at the'control ofiice has its windings included in the control line wire I2; and similarly, at the field station a polar line relay L has its windings included in the line wire l2. These line relays are of the three position biased to neutral polarized type.

Neutral selecting relays S" and S are located respectively at the control ofiice and at the field station for normally connecting the control line wire i2 to the mid tap of the respective batteries TB and PE, or in other words to the common wire Hi. When the contacts of either of these relays are picked up, current impulses are then placed upon the control line wire I2 in accordance with the positions of the polar contact of its respective code sending relay. In the event that both of these selecting relays are energized at the same time, means is provided so that no impulses are transmitted until the operator in the control office has suitably intervened to eliminate'the locked up condition then existing, as more specifically pointed out hereinafter. The

code sending relays CS and CS are respectively selecting relay is energized, time spaced impulses are placed upon the control line circuit having polarities as determined by the corresponding code sending relay, all of which will be more specifically pointed out hereinafter.

Control o jfice equipment-The control ofiice (see Fig. 1) includes, besides the apparatus above enumerated, a quick acting line repeating relay LR of the neutral type, which repeats each energization of the. line relay L irrespective of the polarity with which this line relay is energized. In other words, the quick acting line relay LR, is energized each time the line circuit is energized and is deenergized between the successive impulses.

A slow acting line repeating relay SL of the neutral type is provided with such slow acting characteristics that it does not drop away between the successive energizations of the line repeating relay LR", but once it is energized at the beginning of a cycle, it remains energized until after a predetermined time at the end of the cycle. Also, besides being slow releasing this relay SL is somewhat slow in picking up, although the release period is relatively long compared to the pick-up period.

A checking relay CK of the two position polar magnetic stick type is provided to register or store the particular polarity of the initiating impulse applied to the line circuit at the beginning of each cycle of operation.

Similarly, an impulse storing relay IS is provided to register or storethe particular polarity of each of the impulses applied to the line circuit, so that the polarity of each impulse can be made efiective during the deenergized condition of the line.

A bank of stepping relays'a, b, c and d together with a half step HS serve to mark off the steps of each cycle of operation. The stepping relay bank takes one step each time the line repeating relay LE. is picked up; while the half step relay HS has its contacts actuated to new positions each time the line repeating relay LR is released. This half step relay HS is of the two position polar magnetic stick type. The steps of the cycle are thus marked off so that the code sending relay CS may be distinctively positioned in accordance with the controls to be transmitted.

The impulsing relay IM cooperates with the stepping relay bank and half step relay HS in a manner to time space the impulses applied to the line circuit in accordance with the actual response of the, system in the control oflice.

The control ofiice equipment also includes, be-

sides the various control relays and circuits, a I

various indicating lamps or equivalent means to register the response or conditions of the apparatus at the field station.

As typical of such a control panel, a miniature track switch ts is illustrated as having associated therewith a switch machine control lever SML' and a signal control lever SGL for governing the corresponding track switch and signals in the field location. A starting button SB is provided to be actuated subsequent to the proper positioning of the control levers to thereby initiate the system for the transmission of controls as then set up by the levers. The actuation of the control lever SML to one position or'the other results in the normal or reverse control of the corresponding track switch at the field station, while the actuation of the signal control lever SGL from an intermediate position corresponding to signals at stop, to the right or left clears the signals over the track switch in an east or west bound direction respectively.

A field starting button FSB provides means whereby the operator may cause the field station to transmit its indications although a change in conditions at the station has not previousiy occurred. This field starting button FSB also provides, under certain conditions hereinafter pointed out, means whereby the operator may al- .low the field station to transmit although the line circuits have been locked up upon theoccurrence of a simultaneous start in the control ofi'ice and at the field station. However, during such resulting cycle of operation for the trans mission of indications from the field station, the operator may depress the starting button SB and maintain it in an actuated position until another cycle of operation is initiated, thereby determining that such succeeding cycle of operation shall be for the transmission of control impulses.

The'control machine also includes suitable indication storing relays IR 12R- and IR for storing the various indications transmitted from the field station. The indication storing relay IR stores the indication of the fact of whether the associated track switch is locked or unlocked as indicated by a switch repeating relay WP at the field station, while the normal or reverse position of the track switch is indicated or stored by the relayIRF. The indications of these relays IR and IR may be combined in such a manner that indicator lamps or other types of indicator means may be suitably controlled to inform the operator as to the actual positions of the corresponding track switch TS in the field. For the purpose of illustration, the normal and reverse indicator lamps NI and RI have been shown together with a lock indicating lamp LI.

, The indication storing relay IR is controlled in accordance with the occupied or unoccupied condition of the detector track section associated with the outlying track switch illustrated in Fig. 2, as repeated by a track relay T, so that an indicating lamp OS is controlled in accordance with the passage of a train.

Field station equipment.-'I'he field station (see Fig. 2) also includes, besides the apparatus above mentioned, a quick acting line repeating relay LR which repeats the energizations and deenere gizations of the line circuit as made effective by the line relay L, irrespective of the polarity of the energizing impulses.

A slow acting relay SL of the neutral type repeats the energized condition of the relay LR, but is of the slow picking up and slow releasing type having such characteristics that its releasing period is relatively long compared to its pick-up period so as to maintain the contacts of the relay SL in picked up positions between the successive energizations of the relay LR. In otherwords,

the relay SL is energized at the beginning of each cycle of operation and is maintained energized or picked up throughout the cycle, until the expiration of a predetermined, time after the last energization of the line circuit for the cycle of operation.

A slow acting line repeating relay SLR has characteristics similar to those of the relay SL but repeats the combined conditions of the relays LR and SL in such a manner that the relays SL and SLR are picked up at the beginning of a cycle 'of'operationat substantially the sametime,

but at the end of a cycle of operation, the releasing periods of the relaysSL and SLR arecumulative. 1 I

'Achecking relay CK of the two position polarized type is provided. to register or store the particularpolarity with-which the line circuit is energizedfduring theinitiatingperiod at the be- A stepping relay bank including relays I, 2, 3'

and 4 together with a-half step relay HS is provided to take one step for each energization of the line repeating relay LR so as to markofi the steps upon which the code sending relay CS may be distinctively positioned in accordance with the indications to be transmitted.

A track switch TS is operated by a switch machine SM of any suitable type, such for example as disclosed in the patent to W. K. Howe, No. 1,466,903, dated September 4, 1923. This switch machine may, if desired, be provided with a dual control selector, as disclosed for example in the patenttoW. K. Howe, No. 1,852,573, issued April 5, 1932, soa's to permit the local manual operation of the track switch.

The position and locked condition of the track switch TS is repeated by, the usual switch repeating. relay WP of the polar neutral type. This relay WP is controlled by a suitable polarized circuit (not shown) including point detector contacts or suitable switch box contacts (not shown) so that the relay WP isenergized with current of one polarityor the-other depending upon the nor mal or reverse position of the track switch TS, and so that it is deenergized whenever the track switch TS is unlocked or is'in operation.

The signals IAIB are provided for governing traffic over the main track and over the turn-out track respectively in an east bound direction; while signals 2A-2B are'provided for governing trafiic over the main track or off the turn-out track respectively in a west bound direction. These signals have associated therewith suitable automatic block signalling for providing the safe operation of trains, as shown for "example in my Patent No. 2,082,462 issued June 1, 1937, all of which is unnecessary to be pointed out in detail for an understanding of the present invention.

The track switch TS has associated therewith the usual detector track section having a track battery and a track relay T.- Also, preferably associated with the track switch TS is suitable approach locking and detector locking (not shown) to provide the safe governing of the track switch in accordance with the traflic'conditions.

The track switch machine SM is remotely governed by the operator in thecontrol oflice in accordance with the position of theswitch machine control lever SML,.which control is locally repeated at the switch machine by the switch machine relay' SMR; and similarly, the signals IAlB and 2A-2B are governed remotely in accordance with the signal control lever SGL, which control is repeated locally by the signal relay SR and the direction relay DR. Such-local control'is well understood by those skilled in the art, and has been more specifically disclosed in November 29, 1932.

A change in the condition or the position of the track switch TS is of course repeated by the relay WP, and similarly a change in the condition of the detector track section is repeated by the relay T. Such changes cause the automatic initiation of the system for thetransmission of the indications as then set up. These changes are stored by change relays CH and CH8 until the system has insured the transmission of the new indications.

It is believedthat the nature of the invention, its advantages and characteristic features can be best understood with. further description being set forth from the standpoint of typical operations.

. OPERATION The system of the presentinvention is normally in a condition of restybut may be initiated into a cycle of operation either from the control office or from the field station whenever there are new controls or new indications to be transmitted. Although new controls and indications may simultaneously occur, the present invention is so arranged that only indications or controls may be transmitted during any one cycle of operation; and in such cases where they simultaneously occur, suitablemeans is provided so that the-operator mayace td-alliow the indications to be transmitted followed by a cycle of operation for the transmission of controls.

When a cycle of operation is initiated, a plurality of distinctive impulses (distinctive by reason of their polarity) are placed upon the line circuit for the transmission of either controls or indications. The polarity of these impulses is determined in the case of the transmission of controls in the control ofiicej while-if indications are transmitted, the polarity is determined at the field station. In either case, the duration of the impulses and the time spacing between successive impulses is determined in the control office.

The application of the plurality'of impulses for each cycle of operation causes the step-bystep mechanism to operate sequentially and in synchronism both at the control, ofiice and at the field station. The steps marked off by these step-by-step mechanisms permit the distinctive control of devices on each, step in accordance with the messages transmitted by reason of the distinctive impulses. *In other words,;the stepby-step mechanisms are operated irrespective of the characters of the impulses, while the characters of the impulses serve to carry theproper messages. 7 I

Whilethe system is at rest, or in a. so-called period of blank, the line circuit including line wires Ill and I2 is normally deenergized. Similarly, most of the remaining relays and circuits of the system are normally deenergized with a few exceptions. v

For example, the code sending relay CS in the control ofiice (see Fig. l) is normally energized during the period of blank from (B+) through back contacts l6, l1, l8 and IQ of stepping relaysa, b, c and d respectively, wire 28, front contact 2| of a field starting button FSB, wire 22, back contact 23 of quick-acting line repeating relay LR", wire24, windings of code sending relay CS, to (CN). The current which flows in this circuit is effective to actuate the polar contact of the code sending relay CS to a right hand position.

2,215,437 .thepatent to. S. N; Wight, No..1,889,457, issued Similarly, the code sending relay CS at the field station (see Fig. 2) is normally energized during the period of blank by a circuit from (3+), through back contacts 25, 26, 21 and 28 of stepping relays l, 2, 3 and 4 respectively, wire 29, back contact 30 of quick-acting line repeating relay LR, wire 3|, windings of code sending relay CS, to (CN). The current which flows in this circuit is eifective to actuate the polar contact of the code sending relay CS to a right hand position.

Also, a change relay CH at the field station-is normally energized through a stick circuit closed from through front contact 32 of track relay T, wire 33, front contact 34 of switch rer peating relay WP, wire 35, front contact 36 0f relay CH, wire 31, lower winding of relay CH, to

vIt is, of course, understood that the detector track section associated with the track switch TS is a normally energized track circuit so that the track relay T is normally picked up.

The switch repeating relay WP is energized through a polarized circuit including suitable point detector contacts or the like, so as to be energized: with current of a particular polarity iri'a'cordance' with the normal lock'ed condition of the track switch TS, thereby actuating its polar contacts to right hand positions and actuating its neutral contacts to energized or picked up positions. Whenever the track switch TS is in midstroke or is unlocked, the relay WP is deenergized, but when the track switch TS is in its reverse locked position, the relay WP is energized with current of the opposite polarity, thereby actuating its polar contacts toleft hand positions and its neutral contacts to picked up positions. Although these circuits for the relay WP have not been shown, they will be readily understood by those skilled in the art; I

The half step relay HS is normally energized during the period of blank by a 'circuit from (B+), through back contacts 38, 39, 40 and 4| of stepping relays a, b, c and d, wire 42, windings of relay HS, wire 43, back contact 44 of relay LR to (CN) this circuit is efiective to actuate the contacts of the relay HS toright hand positions preparing the stepping relay bank for the first or initial step of the next cycle of operation. As the half step relay HS at the field station has a normal 'SGL, and then actuates the starting button SB.

It is to be noted, that the operator may move the control levers to such positions as he may desire without the transmission of controls until such time that he actuates the starting button SB. However, such an arrangement is to be considered as merely one embodiment of the present invention, as the system might readily be arranged to be initiated upon the actuation of one or several of the control levers as shown, for example, in my Patent No. 2,159,567 issued May 23, 1939. Y 1

The actuation of the starting button SB, while the system is at rest, causes the energization of the selecting relay S by a circuit closed from The current which flows in through back contact 45 of the starting button SB, wires 46 and 41, back contact 48 of slowacting line repeating relay SL, wires 49 and 5|], windings of relay S to The energization of the selecting relay S closes a front contact included within the line circuit for completing it from the positive terminal of the battery TB, through wire 5|, polar contact 52 of code sending relay CS in a right hand position, wire 53, front contact 54 of selecting relay S wire 55, windings of line relay L wire 56, back contact [5 of impulse relay IM, line wire 12 to the field station, windings of line relay L at the field station, wire 51, back contact 58 of the selecting relay S, wire 59, through the common return line III to the mid tap of battery TB. This initial impulse is positive in character by reason of the normal position assumed by the contact 52 of the code sending relay 05, and thus causes the energization of the line relays L and L in amanner which'effects the actuation of their polar contacts to right hand. dotted line positions.

The energization of the line relay L is in turn repeated by the quick-acting line repeating relay LR by reason of a circuit from through polar contact 60 of relay L in a right hand position, wires 6! and 62, windings of relay LR, to The line repeating relay LR at the field station is similarly energized with polar contact 63 in a right hand position, through circuits obvious from the drawing.

The picking up of front contact 64 of the relay LR energizes the relay SL but as this relay is of the slow-acting type, a certain predetermined time elapses before its contacts assume picked up positions.

Similarly, the picking up of front contact 65 of the relay LR at the field station energizes the slow-acting line repeating relay SL, but as this relay has slow-acting characteristics its contacts do not pick up until after a predetermined time.

Y The picking up of contact 66 of relay LR closes a circuitfrom through front contact 66, wires 61 and 58, windings of relay SLR, to which circuit energizes this relay SLR, but, as it has slow-acting characteristics, its contacts do notpick .up until after a predetermined time. It "is to be noted that these relays SL SL and SLR all preferably have the same slow-acting characteristics and their contacts preferably assume picked up positions at substantially the same time.

During the time following the energization of the line relays U and L, but preceding the picking up of the contacts of the slow-acting relays SL and SL, the checking relays CK and CK are energized with polarities dependent upon the polarity of the impulse placed upon the line circuit.

For example, the relay CK in the control ofiice is energized from (B-), through polar contact H! of relay L in a right hand position, wire H, back contact 12 of relay SL wire 13, windings of checking relay CK", to (CN). The cur rent which fiowsin this circuit causes the relay CK toactuate' its polar contact to a left hand position. I

Similarly, the relay CK at the field station is energized from (B+), through polar contact 14 of line relay L in a right hand position, wire 15, back contact 16 of relay SL, wires 11 and 18, windings of checking relay CK, to (ON). The

M current which flows in this circuit causes the relay CK to actuate its polar contacts to right hand positions. 7

After the predetermined time has elapsed re-- quired for the icking up of the contacts of the relay SL and SL in the control office and at.

the field station respectively, the system is then in readiness to be sequentially and synchronously stepped through a control cycle of operation, as the polarity of the initial impulse placed upon the line circuit during this period is positive in character. This fact is registered in the tWoposition polar checking relays CK and CK, so that after the relays SL and SL have once been energized the nature ofthe cycle of operation is determined or fixed.

In the control office, the checking relay CK completes a stick circuit for the selecting relay S", so that the selecting relay S will remain energized throughout the cycle even after the opening of back contact 48 which is included in its pick-up circuit. This stick circuit is closed from through back contact 19 of stepping relay d, wire Mi, polar contact 8| of checking relay CK in a left hand position, wire 82, front contact 83 of selecting relay S", wires 84 and 50, windings of selecting relay 8, to

It might happen that the preceding cycle of operation was for the transmission of indications, in which case the contacts of the checking relay CK at the field station would be in left hand positions at the beginning of this cycle of operation under consideration. Thus, upon the picking up or actuation of the polar contact 14 of the line relay L to a right hand position in response to the initial energization of the line, energy is momentarily placed on the upper winding of the selecting relay S. As the'checking relay CK is of the two position polarized type, while the selecting relay S is of the neutral type, the contacts of the checking relay CK respond much more quickly than the contacts of a neutral, relay, which prevents the application of energy to the upper winding of the relay S for a length of time sufiicient to actuate the contacts of this selecting relay.

As soon as the slow-acting relays SL and SL have actuated their contacts to picked up positions, the stepping relay banks in the control office and at the field station take the first step. For example, the stepping relay i at the field station is energized by a pick-up circuit from through front contact 85 of relay SL, Wire 86, front contact 87 of relay LR, wire 88, polar contact 89 of relay HS in a left hand position, wire 95, back contacts 9! and 92 of stepping relays 4 and 2 respectively, wires 93 and 94, windings of stepping relay l, to As soon as the contacts of the stepping relay are picked up, a stick circuit is closed for this. relay from through front contact 85 of relay SL, wires 95 and 96, front contact 91 of stepping relay I, wires 98 and 9d, winding of relay l to As the pick-up and stick circuits of the stepping relay a in the control office are substantially identical with those of the stepping relay 1, such circuits will not be pointed out in detail.

The picking up of the contacts of the stepping relay a in the control office completes an energizing circuitfor the impulsing relay 1M from through back contacts IM, ill! and H12 of stepping relays d, c and b respectively, front contact 33 of stepping relay a, wire IM, lower winding of impulsing relay IM, wire i 05, polar contact Hit of relay H8 in a right hand position, wire I01, front contact I08 of relay SL to,

The.

LE to (CN) energization of the impulsing relay IM causes its back contact I5 to be actuated to an open position which deenergizes the line circuit.

When the contacts of the polar relays L and L assume their neutral biased positions, such conditions are in turn repeated by the quick-acting line repeating relays LR and LR.

The dropping of the contacts of the relay LR in the control oflice causes the energizing circuit of the relay HS to be closed, which receives the application of current of opposite polarity by a circuit from (B), through front contact 38 of stepping relay a, back contacts 39, 46 and M of stepping relays b, c and d respectively, wire 42, windings of relay HS", wire 43, back contact 44 of quick-acting line repeating relay The current which flows in this circuit causes the half step relay 1-18 to actuate its polar contacts to left hand dotted line positions. Similarly, the polar contact 89 of relay HS is actuated to an opposite position at this time with the relay LR deenergized, as will be obvious from the drawings.

The movement of polar contact I86 of relay HS to a left hand position opens the energizing circuit for the impulsing relay IM, so that the contact I of this relay IM then assumes a deenergized position for energizing the line circuit with an impulse having a polarity determined in accordance with the position of the polar contact 52 of code sending relay CS".

During the time subsequent to the deenergization of the line repeating relay LR but prior to the actual closing of back contact I5, the code sending relay CS is energized with current of a polarity determined in accordance with the control desired to be transmitted upon the next step. For example, on this step with the contacts of the stepping relay a picked up, the code sending relay CS is energized with current of a polarity dependent upon the position of the switch machine control lever SML. If the switch machine control lever SML is in a left'hand normal position, current of positive polarity from (B+) is applied to this code sending relay; but, if the lever SML is in a right hand reverse position, current of negative polarity from (B) is applied to this code sending relay. Thus, a circuit is closed from (B+) or (B) through lever contact I69 in a left or right hand position respectively, wire III], front contact I6 of stepping relay a, back contacts I'I, I8 and I9 of stepping relays b, c and d respectively, wire 20, front contact 2| of field starting button FSB, wire 22, back contact 23 of relay LR, wire 24,windings of code sending relay CS to (CN). This application of potential to the code sending relay CS causes the actuation of its polar contact to a proper position for determiningthe desired polarity of the next impulse applied to the line circuit upon the closure of back contact I5 of impulsing relay IM. As the relay HS must be actuated to a new position and the relay IM dropped away before the contact 52 of relay CS is effective, there is a sufficient margin of time to insure that it has properly responded.

Upon the closure of back contact I5, the line relays L and L are then energized with current of a polarity dependent upon the position of contact 52, but irrespective of the particular polarity of the impulse, the quick-acting line repeating relays LR and LR are energized and their contacts are immediately picked up.

Immediately upon the picking up of the contacts of the relay LR at the field station, the

impulse storing relay IS is energized with positive or negative current dependent upon whether the impulse appliedto the line circuit is positive or negative in character. For example, depending upon whether the impulse is positive or negative, an energizing circuit for relay IS is closed from (B+) or (B), through polar contact I4 of line relay L in a right or left hand position, wire I5, front contact I6 of relay SL, wire III, front contact H2 of relay LR, wire II3, back contact II4 of selecting relay S, wire II5, windings of relay IS, to (CN). The current which flows in this circuit actuates the polar contact of relay IS to a right or left hand position depending upon whether it is positive or negative in direction, and the contact remains in such position in readiness for the execution of the message during'the following deenergization of the line circuit.

This energization of the line repeating relays LR and LR causes the second stepping relays to be energized. For example, the stepping relay 2 has a pick-up circuit closed from through front contact 85 of'relay SL, wire 86, front contact 8? of relay LR, wire 88, polar contact 89 of relay HS in a right hand position, wire I I6, back contact II? of stepping relay 3, front contact II8 of stepping relay I, wires H9 and I20, windings of stepping relay 2, to As soon as the contacts of stepping relay 2 pick up, a stick circuit is closed from through front contact 85 of relay SL, wires 95, I2I and I22, front contact I23 of stepping relay 2, wires I24 and I28, windings of stepping relay 2, to

In a similar manner, the stepping relay b in the control office is picked up and stuck up.

The picking up'of the stepping relay 1) closes an energizing circuit for the impulsing relay IM from through back contacts I06 and IIlI of stepping relays d and c respectively, front contact I92 of stepping relay 2), wire I25, upper winding of impulsing relay IM, wire I26, polar contact I66 of realay HS in a left hand position, wire I81, front contact I68 of slow-acting line repeating relay SL to The impulsing relay thus energized actuates its contact I 5 to a picked up position opening the line circuit, the deenergization of which is repeated in the control office and at the field station by the line relays L" and L respectively, which is in turn repeated by the relays LR and LB.

1 An execution circuit closed during this period of time in which the line circuit is deenergized and the stepping relay 2 is picked up, governs the switch machine control relay SMR. This is accomplished by the application of positive or negative potential upon the relay SMR in accordance with whether a positive or negative impulse is stored in the impulse storing relay IS, as

determined by the preceding energization of the line circuit in accordance with the position of the control lever SML. For example, the relay SMR is energized from (B+) or (B), through polar contact I21 in a right or left hand position, wire I28, back contact I 29 of selecting relay S, wire I3I), back contact I3I of relay LR, wire I32, front contact I33 of relay SL, wire I34, back contacts I35 and I36 of stepping relays 4 and 3 respectively, front contact I3! of stepping relay 2, wire I 38, windings of relay SMR, to (CN). The current which flows in this circuit actuates the polar contact of the relay SMR to a right or left hand position depending upon whether positive or negative potential respectively is applied thereto.

With polar contact I39 of the switch machine control relay SMR in a right hand position, positive potential is applied to the normal operating Wire N of the switch machine SM; but with polar contact I39 of the switch machine control relay SMR in a left hand position, positive potential (-1-) is applied to the reverse operating wire R of the switch machine SM. This energization of the normal and reverse wires N and R results in the corresponding operations of the switch machine SM for moving the track switch TS to normal or reverse locked positions in the usual manner.

In brief, the positioning of the control lever SML determines the polarity applied to the switch machine control relay SMR, which in turn governs the operation of the switch machine. Obviously, if the control lever is moved to a new position, the track switch will be operated; but if it is left in a former position during a cycle of operation, the track switch will remain in such former position.

During this deenergized period of the line with the relay LR deenergized, the relay HS receives current of the opposite polarity from (B+) through front contact 39 of step-ping relay 1); and similarly the contact 89 of relay HS is actuated to a new position. Also, simultaneously therewith, the code sending relay CS is energized in accordance with the position of the contact I40 of signal lever SGL to determine the polarity of the next impulse applied to the line circuit upon the closure of back contact l5 of the impulsing relay IM. The polarity of such impulse is then made effective upon the deenergized period of the third step to govern the signal relay SR. In other words, the step-by-stepoperation of the stepping relay banks occurs sequentially and in synchronism for, as many steps as required to transmit the control conditions to the field station. In this case, the relays SR and DR, for controlling the signals at the field station, are controlled upon the third and fourth steps respectively in accordance with the position of the control lever SGL in a similar manner as explained for the relay SMR.

This transmission of controls, as above explained in detail, may be briefly considered by saying that the code sending relay CS is positioned during each deenergized period of the line for determining the character of the next impulse, while the character of such next impulse is stored in the impulse storing relay IS for execution during the succeeding deenergization of the line circuit, to the particular function control relay, such as relay SMR, for which it is designated.

This transmission of controls continues until the predetermined number of steps have been taken, which, by way of example, has been specifically illustrated as including foursteps, only three of which are employed for control impulses. as the application of the first impulse to the line circuit is employed for initiation purposes and determining the particular character of the operating cycle, thus initiated.

When the last stepping relay is picked up in the control oiiice, stepping relay d in this case, a circuit is completed for the impulsing relay IM through front contact I90, which circuit is maintained until the line circuit has been deenergized for a predetermined period of time to mark off the end of that cycle of operation, thereby opening front contact I08 of relay SL More specifically, the picking up of front contact M of stepping relay d fails to place current of the opposite polarity on the relay HS upon'the deener'gization of the relay LR", so that the energizing circuit for the impulsing relay IM is not broken by the operation of polar contact I06 to an oppo-. site position, as usually occurs on the preceding steps.

The picking up of the contacts of the relay d also causes the deenergization of the selecting relay S by opening its stick circuit at open back contact 19 allowing its contacts to drop away.

The deenergization of the line circuit is repeated by the quick-acting line repeating relays LR and LR, as previously, but in this case the deenergized condition of the line continues until a sulficient length of time is marked off for the contacts of the relays 'SL and SL .todrop away, as their energizing circuits are respectively opened at front contacts 64 and 65. Although the relays SL and SLR pick up together, the relay SLR adds its drop-away time to the drop-away time of the relay SL, as its energizing circuit includes, besides front contact 66 of relay LR, the front contact Ml of relay SL. In other words, the release or drop-away time of the relays LR, SL and SLR at the end of an operating cycle are cumulative for reasons hereinafter pointed out.

The drop away of the relay-SL in the control oifice and the relay SL at the field station causes the dropping away-of the stepping relays at both locations, and the return of the system to a normal condition of rest. The drop away of the relay SL in the control oifice permits the selecting relay S to be again picked up providing the starting button SB is actuated by the operator for initiating another such cycle of operation for the transmission of control impulses; while the drop away of the relay SLR at the field station permits the selecting relay S to be picked up providing a new indication has occurred causing the energization of the relay'CHS for initiating .a; cycle for the transmission of indication impulses.

Transmission of indications-Whenever thesystem is in the period of blank it may be initiated from a field station either in response to some automatic change in traflic conditions, or in response to the operation of a traffic controlling device manually governed from the control ofiice when such device is caused to assume a new position.

For example, the operation of the track switch TS from a normal position toa reverse position, in response to thecontrol of lever SML, as above explained, deenergizes the relay WP during such reverse operation, but energizes it with current of the opposite polarity at the completion of such operation. The deenergization of the relay WP as well as its reenergization momentarily deenergizes the stick circuit of the change relay CH during the movement of contact 34 from a front to a back contacting position, or vice versa. As the change relay CH is of the relatively quickacting type this momentary deenergization is of sufiicient duration to allow the contacts of the change relay to drop away, permanently opening the stick circuit of this relay until it is again energized, or resensitized so to speak, by energization of its pick-up circuit.

The change relay may also be deenergized upon the change of traflic conditions, as for example the deenergization of the track relay T upon the passage of a train over the associated detector track circuit, when the traffic controlling devices have been properly governed for the movement of trafiic in accordance with the usual practices.

In brief, the stick circuit for the change relay CH is carried through front and back contacts ofthe relay WP and the track relay T, and may similarly be carried through like contacts of other traflic controlling devices associatedwith this field station. Irrespective of the particular change which occurs, the deenergization of the change relay CH closes a pick-up circuit for the change storing relay CHS, which in turn energizes the pick-up circuit of the change relay as well as energizing the initiating circuit of the selecting relay S.

Assuming that the system is at rest, and that a change in indication conditions is incurred by the deenergization of the track relay T, for example, then the CHS relay is energized by a circuit from ,through back contact 32 of track relay T, wire 33, front contact 34 of relay WP, wire 35, back contact 36 of change relay CH, wire I42, upper winding of relay CI-IS, to The relay CHS, thus energized, actuates its contacts to picked up positions, thereby closing its stick circuit from through back contact I of relay S, wires I5I, I52 and I53, front contact I54 of relay CHS, wire I55, lower winding of relay CHS, to This circuit also has applied to wire I52 through back contact I56 of stepping relay 2.

The pick-up circuit for the relay CH is now closed from through back contacts I56 and I56 of relays S and 2, respectively in multiple, wires I52 and I51, front contact I58 of relay CHS, wire I59, upper windings of relay CH, to The closure of the front contacts of relay CHS also completes a pick-up circuit for the relay S, as the system is at rest, from through front contact I60 of relay CHS, wire I6I, back contact I62 of relay SLR, wires I63 and I64, lower winding of relay S, to

The picking up of the contacts of the relay S in response to this energizationaccomplished by the relay CHS, closes front contact 58 of relay S,-so as to place a positive impulse upon the line circuit from the battery F3 in accordance with the normal position assumed by the polar contact of the relay CS during the normal at rest condition of the system. This line circuit is closed from the positive terminal of the battery FB, through polar contact I65 of relay CS in a right hand positio wire I66, front contact 58 of relay S, wire 51, windings of relay L, line wire I2 to the control oflice, back contact I5 of relay IM, wire 56, windings of relay L, wire 55, back contact 54 of relay S, wire- I61, to the common wire I6 thence to the mid tap of battery FB at the field station.

Although this impulse is termed a positive impulse, its actual direction isopposite to the direction of current flow set up by a positive impulse from the tower battery TB, so that the'contacts of the polar relays L and L are actuated to left hand dotted line positions. However, for convience in the description, this may be considered as a positive impulse, as the polarities on contact 10 of relay L are so arranged that a corresponding potential is applied to the execution circuits for the indication storing relays IR (with suitable exponent). Thus, a circuit is completed from (B), through polar contact 14 in a left hand position, wire 15, back contact 16 of relay SL, wires 11 and 18, windings of relay CK, to (CN). The current flow in this circuit actuates the contacts of the relay CK to left hand positions. This further insures that the relay S is picked up by reason of a circuit closed from (B), through polar contact 14 of relay L in a left hand postion,

wire 15, back contact 16 of relay SL, wires 11 and I68, polarlcontact I69 of relay CK in a left hand position, wire I10, upper winding of relay S, to (CN) Similarly, in the control ofiice the actuation of the contacts of the relay L by current flowing in the line circuit, as above pointed out, energizes the relay CK". by a circuit from (B+), through polar contact 10 of relay L in a left hand position, wire 1I, back contact 12 ofrelay SL wire 13, windings of relay CK, to (CN). Current flowing in this circuit actuates the polar contac 8| to a right hand position. r

The energization of the line circuit, as indicated by' the relays L and L, is repeated by the quick-acting line repeating relays LR and LR immediately, while a predetermined time thereafter; the energization of the respective slowacting relays SL and SL is efiective to pick up their contacts. During the time subsequent to the picking up of the contacts of the relays L and L, the relays CK and CK are controlled as above pointed out, so that upon the picking up of :the contacts of the relays SL andSL, the character of the cycle has been determined or registered by these checking relays, and the sys tem is in readiness for taking the first step.

Upon the picking up of the contacts of relay SL, astick circuitis closed from through front contact ill of relay SL, Wire I12, polar contact I 13 of relay CK in a left hand position, wire E14, front contact I15 of relay S, wires I16 and I64, lower winding of relay S to As the relays SL and SLR have practically the same slowacting characteristics, they are energized or picked up at practically the same time, so that. the pick-up circuits of the relay S are opened at substantially the same time. However, for the purpose of preventing a momentary deenergization of the relay S, the front contact I1I ofrelay SL is preferably closed before the back contact 16 of the relay SL is opened.

With the relays SL and SL' at the control ofiice and field station respectively energized, pick-up and stick circuits are closed for the first stepping relays, as previously pointed out.

The picking up of the stepping relaya in the controlrofiice eifects the energizationof. .the impuls ing relay IM, which in turn opensback con--.

tact I5 and deenergizes the line circuit, as previously explained ,This condition is repeated by" the line relays L and L, as well as by the relays LE and LR.

During this deenergized condition of the line circuit, the code sending relay CS at the field station is energized with current of a polarity in accordance with the energized or deenergized condition of the relay WP. For example, if the track switch is locked, the relay WP is energized and (3+) is applied to this relay CS; While on the other hand, if the track switch TS is unlocked, the relay WP is deenergized and (B-) is applied to this relay CS. This energizing circuit for the relay CS is closed from (B+) or (B-),' through front or back contact I 11 respectively of relayWP, wire I18,'front contact 25 of stepping relay I, back contacts 26, 21 and 28 of stepping relays 2, 3 and 4 respectively, wire 29, back contact 36 of relay LR, wire 31 windings of relay OS, to (CN).

In either case, the relay CS is energized with current of a particular polarity as soon as the contacts of the relay LR drop awayand prior to the time of the closure of back contact I5 upon the drop away of this contact subsequent to the deenergization of the relay IM. In other words, the relay CS is controlled simultaneously with the actuation of the contacts of the half step relays HS and HS to new positions, in a manner similar to that explained for the relay CS in the control ofiice during a control cycle of operation.

The response of the relay HS deenergizes the relay IM, so as to energize the line circuit, as above explained.

Thus, dependent upon the energized or deenergized position of the relay WP, the line circuit receives positive or negative potential from the battery FB. A positive impulse actuates the polar contacts of relays L and L to left hand positions; while a negative impulse actuates the polar contacts of these relays to right hand positions. But, irrespective of the particular polarity placed upon the line circuits, it is repeated by their respective quick-acting line repeating relays LR and LR causing the next step to be taken both in the control ofiice and at the field station.

The particular polarity of this line circuit impulse is stored in the control ofiice in the impulse storing relay IS by the energization of this relay with positive or negative current from (13+) or (B-) depending upon the character of the impulse on the line circuit, through polar contact Iii of line relay L in left or right hand positions respectively, wire II, front contact I2 of relay SL, wire I], front contact I8I of relay LR, wire 182, back contact I83 of relay S", wire I84, windings of the relay IS to (CN) It is to be noted that the impulse storing relay IS at the field station is not responsive to these energizations of the line circuit during an indication cycle of operation, as its controlling circuit is opened at the back contact H t of relay S. This condition corresponds to the unresponsiveness of the relay IS to control impulses on the line circuit by reason of open back contact I83 of relay S during a control cycle of operation.

This energization of the line relays L and L repeated by the relays LR and LR also effects the picking up of the stepping relays b and 2 at the control ofiice and at the field station. The picking up of the stepping relay b causes in the control ofiice the energization of the inip-ulsing relay IM and the picking up of contact I 5 which again deenergizes the line circuit. This condition is in turn repeated by the various line repeating relays. The deenergization of the line relay LR closes a circuit for the indication storing relay 1R so that the message or indication temporarily stored in the impulse storing relay IS may be executed, or permanently stored in the relay IE until a new indication is transmitted. For example, depending upon Whether the relay IS was energized with current of positive or negative polarity during the energized condition of the line, (3+) or (13-) is applied through polar contact I99 of relay IS in a right or left hand position respectively, wire it! ,back contact I92 of relay S, wire I93, back contact I96 of relay LR, wire 95, back contacts I85 and I9'I of stepping relays d and 0 respectively, front contact I98 of stepping relay b, wire I99, windings of relay 1R to (C'N). The application of positive potential (3+) to relay 1R actuates its contacts to left hand positions; while the application of negative potential (B) to relay 1R actuates its contacts to right hand positions.

In other words, depending upon whether the relay WP is energized or deenergized, current of one polarity or the other is placed upon the relay CSduring one deenergized period of the line circuit which determines the polarity of the following energized period of the line, this particular polarity being stored in the impulse storing relay 1S Then the relay IE is energized upon the following deenergized period of the line in ac cordance with the particular polarity stored in.

station during an indication cycle of operation, as.

now being described, which condition prevents the energization of the function control relays", such as relays SMR, SR and DR, by reason of open back contact I29 of selecting relay S.

During this deenergized period of the line circuit with the second stepping relays b and 2 picked up, and simultaneous with the energization of the indication storing relay 1R in accordance with the position of contact I of relay IS", the code sending relay CS at the field station is being positioned in accordance with the next indication to be transmitted. In this case, the relay CS is" controlled in accordance with the normal or reverse position of the track switch TS as indicated by the relay WP. For example, if the track switch is in a normal position, the relay CS is energized with current of positive polarity (13+) while if the track switch TS is in a reverse position, the relay CS is energized with current of negative polarity (B) In other words, dependent upon the position of the track switch TS, the relay CS is energized from (B+) or (B), through polar contact 202 of relay WP in a right hand or left hand position respectively, wire 2B3,

front contact 26 of stepping relay 2, back contacts 2'! and 28 of stepping relays 3 and 4 respectively, wire 29, back contact" 3i] of relay LR, wire 3!, windings of code sending relay CS, to (CN).

Also, simultaneously with the actuation of the code sending'relay CS at the field station and the indication storing. relay at the control office, the half step relays HS and HS are suitably positioned, as previously described.

The response of the half step relay HS results in the deenergization of the impulsing relay IlVl closing back contact I5 and thereby energizing the line circuit with a polarity in accordance with the position of contact I65 of the code sending relay CS in the field, which is now positioned in.

accordance with the normal or reverse position of the track switch TS as indicated by the polar contact 262 of relay WP.

The energization of the line circuit results in the picking up of the third stepping relays c and 3, as well as the energization of the impulsing relay IM. However, prior to the energization of the relay IM, the impulse storing relay IS is energized in accordance with the polarity of the impulse applied to the line circuit, as previously described.

Thus, upon the deenergization of the line cir-- cuit. the indication storing relay 1& is energized in accordance with the position of the polar contact I90 of relay IS while at the field station, the code sending relay CS is being positioned in accordance with the next indication to be transmitted. The response of the half step relays HS and HS conditions the system for the next energilay IM.

In a similar manner, as above explained, the step-by-step operation continues, and an indication is transmitted on each step, until a sufiicient number of steps have been taken to transmit such indications as may be desired. In this case, a system has been illustrated as having only three indication transmitting steps, but it is to be understood that the system may be readily extended to include as many indication steps as may be found necessary in actual practice.

When the system has taken the last step (fourth in the present embodiment), the line circuit is maintained deenergized for a sufiicient period of time to allow the drop away of the contacts of the slow-acting relays SL1 and SL. This is by reason of the continued energization of the impulsing relay IM on the fourth step, due to the absence of the application of current of the opposite polarity to the half step relay HS through contact 4!, as explained in connection with the control cycle of operation. The deenergization of the slow-acting relays SL and SL causes the dropping away of the stepping relay banks and the selecting relay S, together with the positioning of the various other relays to their normal positions.

Assuming the track switch TS to be in a normal position during such cycle of operation, positive impulses will be placed upon the first and second indication steps so that the indication storing relays IR and IE will both receive positive impulses. This positions their respective polar contacts 2! and 2 H in left hand positions to complete a circuit for the normal indicator NI from through polar contact 2I0 of relay 1B in a left hand position, wire 2|2, polar contact 2!! of relay 1R in a left hand position, normal indicator NI, to Thus, the operator is in-. formed of the normal position of the switch TS.

On the other hand, if the track switch TS is in a reverse position, a negative impulse will be transmitted on the second step and the indication storing relay IE will be energized with a negative potential actuating its contact 2 to a right hand position. This causes the energization of the reverse indicator RI through a circuit obvious from the drawings.

In. the event that the track switch TS is unlocked and the relay WP is deenergized, a negaposition.

through polar contact 2!!! in a right hand positive impulse will be transmitted upon the first step resulting in the application of negative potential to the indication storing relay 1R which actuates its polar contact 2l0 to a right hand This applies potential from tion, lock indicator LI, to The energization of this indicator displays to the operator that the track switch TS is unlocked.

If on the third step the track relay T is energized, a positive impulse will be transmitted actuating the polar contact 2l3 of the indication storing relay IE to a left hand position; while if the track relay T is deenergized, a negative impulse will be transmitted actuating the polar contact 2 iii of relay IE to a right hand position. With polar contact 2l3 in a right hand position, positive potential from is applied to the indicator OS advising the operator of the presence of a train on the associated detector track section.

It is to be understood of course that although merely indicator lamps have been illustrated for advising the operator of the conditions at the zation of the line circuit by deenergizing the refield station, other suitable indicator means such as audible warnings, miniature movable track switch points, or the like, may be employed as desired.

Indication cycle initiated from the control 017ice.Inasmuch as the indications of the trafilc conditions along the trackway may occur at any time and are not under the control of the operator, it may happen that such a change will occur simultaneously with the actuation of the starting button SB for the transmission of controls from the control oflice. The present invention provides special means for such a case, so that the system may be set into operation irrespective of the locked up condition initially brought about under these circumstances.

It may also happen that for one reason or another, the operator may desire to check the conditions of the apparatus and trafiic indications at the field station, so as to be sure that he is setting up the proper routes. Under these circumstances, there may be no automatic change in conditions at the field station to initiate the system into operation, so that a manual act upon the part of the operator is required to start the system in a special way in order to accomplish an indication cycle of operation.

These various operating conditions will probably be best understood by a description of typical cases. 1

Let us assume that the system is at rest and that the operator desires to check the indication conditions as now set up at the field station. To do this, he actuates the field starting button FSB to a depressed position. This manual manipulation is effective to energize the selecting relay S" and to simultaneously apply negative potential to the code sending relay CS Inasmuch as the code sending relay CS is of the two position polarized type, while the relay Sis of the neutral type, the code sending relay CS responds more quickly and its polar contact 52 assumes a left hand position in readiness for placing a negative impulse upon the line circuit prior to the closure of front contact 54 of relay S More specifically, negative potential is applied to relay CS by a circuit from (B), through back contact 2| of lever FSB, wire 22, back contact 23 of relay LR wire 24, windings of code sending relay CS", to (CN) Energy is applied to the pick-up circuit of the selecting relay S from through back contact 200, wires 2M and 41, back contact 48 of relay SL, wires 49 and 50, windings of relay S to The picking up of contact 54 of the relay S subsequent to the response of the polar contact 52 of relay CS places a negative impulse on the line circuit, that is, it causes current to flow in the line circuit in a direction which corresponds to the direction of current flow set up whenever the system is initiated into a cycle of operation automatically from the field station. Therefore, the polar contacts of the line relays L and L are actuated to left hand positions, which conditions are, of course, repeated by their respective quick-acting line repeating relays LR and LR as well as by their respective slow-acting line repeating relays SL and SL, all in the usual manner as above described.

However, during the time subsequent to the actuation of the polar contacts of the line relays to left hand positions, but prior to the picking up of the contacts of the slow-acting line repeating relays SL and SL, the respective checking relays CK and CK are energized with polarities corresponding to those applied when the system is initiated automatically from the field station. For example, in the control office, (B}-) will be connected to the relay CK through polar contact if! in a left hand position, and back contact 12 of relay SL, thereby causing its contact 8! to be actuated to a right hand dotted line position; while at the field station, (B-) will be connected to the relay CK through polar contact 14 of relay L in a left hand position and back contact I6 of relay SL, thereby causing its polar contacts 159 and H3 to be actuated to left hand positions.

With contact 16% of relay CK in a left hand position and polar contact 14 of relay L in a left hand dotted line position, (B) is connected to the upper winding of the selecting relay S, through a circuit previously described, until the contacts of the slow'acting relay SL are picked up. This application of current to the relay S actuates its contacts to picked up positions, and in so doing the positive terminal of the field battery PE is connected to the line circuit through front contact 58 and polar contact i555 of relay CS in a right hand position.

It is noted, that the negative terminal of the battery TB is also connected to the line circuit and that the potentials of these batteries TB and PB are additive, thereby increasing the line current to substantially double its normal value. Although, it would not be particularly desirable to maintain such a condition of high'current value in the line circuit for a protracted period of time, the actual period of time during which this condition exists, that is, during the pick-up period of the slow-acting relay SL plus the drop-away period of the relay S, is in practice not usually more than one second. Also, the line relays are so constructed as to be unharmed by this initial current value.

Upon the picking up of the contacts of the relay SL in the control oifice, the pick-up. circuit of the selecting relay S is opened at back contact 48, allowing the contacts of relay S to drop away, as its stick circuit is not completed with'polar contact 8i of relay CK in a right hand position. The closure of back contact 54 I of relay S removes the negative terminal of the tower battery TB from the line circuit, so that a normal current value is established in the line circuit by the field battery FB.

At the field station the picking up-of the contacts of the relay SL opens the pick-up circuit of the relay S at back contact '36 but closes its stick circuit through front contact 51!, polar contact N3 of relay CK in a left hand position, and front contact N of relay- S, as previously described,

In other words, the same conditions are established in the control oifice and at the field station as when an automatic initiation of the systern occurs at the field station, so that with the selecting relay S in the control office deenergized, and the selecting relay S at the field station energized or picked up, the system is then in readiness to transmit its indications without further manual intervention but in the usual way, as previously described.

It will be noted, that during 'the initiation of the system under the above circumstances, the line circuit is momentarily interrupted by the changing of the contact 58 of relay S from a back point to a front point, and similarly by the changing of the contact 54 of relay S from a a front point to a back point, but these momentary interruptions are of. such relatively short duration that they are not repeated by the line relays L and L. v

It is believed that the resulting cycle of operation for the transmission of indications will be readily understood by reference to the cycle of operation already described.

As above mentioned, it may happen that the operator actuates the starting button SB at the same time that the change storing relay CHS is picked up. In such a case, the selecting relays S and S are simultaneously energized, and their contacts assume picked up positions at substantially the same time, thuswconnecting the positive terminals of both the battery TB and FB to the line circuit through their respective front contacts 54 and 58. The potentials of the two batteries oppose each other so that there is no resulting current fiow in the line circuit, and the system remains in a static condition. The operator noticing this condition, either because of the failure to receive proper indications, or by reason of a special operation indicator such as shown, for example, insthe patent to W. D. Hailes et. al. No. 2,170,141 issued August 22, 1939, actuates the field starting button P813 to a depressed position which reverses the polarity applied to the code sending relay CS. This actuates! the polar contact 52 of relay CS to a left hand position connecting the negative terminal of thebattery TB to the line circuit, so that there is a resulting current flow in the line circuit in a direction corresponding to that current fiow established by an automatic initia tion from the field station, which current flow is of substantially double the normal current fiow, as the potentials of these batteries are additive. In other words, the same conditions are now set up as if the operator had originally actuated the field starting button FSB.

More specifically, this direction of current flow in the line circuit is registered by the relays OK and CK so that upon the picking up of the relays SL and SL, the pick-up and stick circuits of the relay S will be opened, while the stick circuit for the relay S will be maintained closed. After the slow-acting relays have picked up their contacts,

the first stepping relays are picked up and the cycle of operation continues for the transmission of indications in the usual way. When the second step is taken the selecting relay S being picked up, the relay CHS is deenergized, as the back contacts I50 and l 56 are both open.

It will be noted, that the field starting button F513 is of the self-restoring type, so that the operator must hold it in an actuated position until the slow-acting relays SL and SL have been energized for a sufiicient time that their contacts will assume picked up positions. In actual practice, this time period is so short that the operator does not find it necessary to actuate the button FSB for an undue length of time. If, in some cases, it is found that the operator does not have time .or fails to actuate the button FSB for a sufficient period of time, automatic means can be supplied to maintain this starting condition until the relay SL9 is picked up, but as this is a special manual operation required only in unusual cases, such automatic means is not considered as ordinarily,

required.

It is believed unnecessary to describe in detailthe resulting transmission of indications during the cycle initiated, as just described, but it will be pointed out that at the end of the operating cycle,

the operator may'cause the next cycle of opera-f tion'to be a control cycle, irrespective of the fact that some other change may have occurredat the field station which would normally cause the next cycle to be an indication cycle. This function of the system is accomplished more particularly by reason of the added release time of the relay SLR over or beyond the drop away time of the contacts of the relay SL. 7

More specifically, after the operator has actuated the field starting button PS3 to cause the operation of the system in the event of a simultaneous start from the control office and from the field station and has again released the button FSB, when the system has started, he immediately actuates the starting button SB and continues to hold it in an actuated position. This actuation of the starting button SB is not effective during the resulting cycle of operation, as the back contact 48 of relay SL is open.

Upon the dropping away of the contacts of the relays SL and SL at the end of such cycle of operation, however, the selecting relay S is immediately picked up, which places a positive impulse upon the line circuit because the code sending relay CS has been returned to its normal position even prior to the drop away of the stepping relay contacts. This is accomplished by reason of a circuit which is completed for this code sending relay CS as soon as the last step has been taken and the line circuit deenergized with the back contact 23 of relay LR. closed. This circuit is closed from (3+), through front contact l9 of stepping relay (1, wire 20, front contact 2| of field starting button FSB, wire 22, back contact 23 of relay LR wire 24, windings of relay CS, to (CN) In other words, at the end of the indication cycle of operation, the relay SLr drops away in the usual manner, deenergizin'g the selecting relay S, but the relay SLR. does not drop away until a predetermined time after the contacts of the relay SL are in deenergized positions, which prevents the relay S from being again picked up for a prolonged period of time, even if the relay CHS is energized. During this'prolonged period of time,-

the relay S in the control ofiice may be picked up, which, with the code sending relay CS returned to a normal position, places a positive impulse upon'the line circuit for initiating the system from the control office, thereby causing a control cycle of operation and preventing the initiation from the field station.

The field station cannot interfere in such a case, as the positive impulse is repeated by the relays L and LR prior to the drop away of the contact I62 of the relay SLR, which prevents the contacts of the relay SLR. from assuming deenergized positions.

Such an initiation of a control cycle is registered by the relays CK and OK, and the system continues to function for the transmission of controls in a manner similar to that already described. If desired, the operator may transmit controls for as many cycles as conditions may warrant without the interruption by the field station, and. during such time the change storing relay CHS, if there are indications to be transmitted, will remain picked up because its stick circuit has not been opened at the back contact I50 of the relay S.

Summary.-In general, the system of centralized traflic control contemplated by this invention is particularly adapted for interconnecting a control office and a single outlying field station, irrespective of the number of devices to be controlled at that station or the number of devices having indications to transmit to the control office. This system is characterized by the fact that the communication is established between the control office and the outlying field station over only two line wires with the line circuits normally deenergized while the system is at rest.

The present invention also provides suitable means whereby only controls or indications may be transmitted during any one particular operating cycle, together with means for initiating a cycle for controls in the control ofiice; for automatically initiating the cycle of indications at a field station; or for manually initiating a cycle for indications in the control ofiice. In other words, although the system is normally at rest, it

may be initiated into operation for transmission of messages in either direction under every condition which is normally encountered in practice.

The system of the present invention employs a tower battery and a field battery for supplying impulses of distinctive polarities to the line circuits for transmitting the messages. Such an arrangement means a definite and positive response which is a distinctadvantage for a system of this character.

Various other features of the system, embodye ing the present invention may be said to reside in the detail circuits and devices of the system.

Having thus described a centralized traflic control system as one specific embodiment of the present invention, it is desired to be understood that this form is selected to facilitate in the disclosure of the invention rather than to limit the number'of forms which it may assume; and, it is to be further understood that various modifications, adaptations and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing fromthe spirit or scope of the present invention, except as limited by the appended claims.

What I claim is:

1. In a remote control system for railroads, a control office, a field station, a line wire extending from said control oifice to said field station, a return line wire extending from said control ofiice to said field station, a line relay at said control oifice and at said field station included in series with said line wire, a normally closed impulsing contact included in series with said line wire, a selecting contact at said control office for normally connecting said line wire to said return line wire, a selecting contact at said field station for normally connecting said line wire to said return line wire, means at said control oflice for connecting a battery between said line wire and said return line wire when said selecting contact at said control ofi'lce is picked up, means at said field station for connecting a battery between said 'line wire and said return line wire when said selecting contact at said field station is picked up, means at said control office for intermittently opening said impulsing contact when either one of said selecting contacts is picked up, and means responsive to the alternate energization and deenergization of said line relays when a selecting contact is picked up and said impulse contact is being opened and closed. a

2. In a remote control system of the selector type; the combination with a control office and a field station; of a single line circuit connecting said control office with said field station; step-by-step means at said control oifice and at said field station responsive to series of impulses on said line circuit to operate through cycles of operation irrespective of their character; battery sources at said control office and at said field station; selecting means for. initially connecting said battery sources in said line circuit with a particular polarity, whereby when said sources at said control office and at said field station are both connected in said line circuit there is no current fiow; impulsing means at said control ofiice for opening said line circuit when there is a current flow in said line circuit for a predetermined time and for opening said line circuit at time spaced intervals thereafter, whereby a plurality of impulses are placed on said line circuit to comprise a cycle of operation; code sending means at the control olfice and at said field station for determining the polarity of each impulse except the first, said code sending means at said control oifice or at said field station being chosen by said selecting means, whereby messages are transmitted to and from said field station and said control office during separate cycles of operation; and means manually operable to reverse the polarity of the initial connection of said source in said control office.

3. In a remote control system comprising two stations connected by a single line circuit, transmitting means at each station for delivering series of code elements to said line circuit, means at one station for time spacing the code elements of each series irrespective of which transmitting means is eliective, means at each station for imparting a different character to the first element of each such series originating at that station, and means at each station responsive to the character of said first element of a series to render inerfective the transmitting means at such station when the character of the first element is determined at the other station.

4. In a remote control system comprising two stations connected oya single line circuit, transmitting means at each station for delivering series of code impulses to said line circuit, means at one station for time spacing the code impulses of each series irrespective of which transmitting means is effective, means at each station for imparting a particular polarity to the first impulse of each series originating at that station, and means at each station responsive to the polarity of said first impulse to render effective or ineffective the transmitting means at such station, depending upon the polarity of such first impulse.

5. In a remote control system for railroads, a plurality of stations connected by a single line circuit, transmitting means at each station including a source of current for impressing a series of distinctive impulses on said line circuit, means at one station for time spacing the code impulses of each series irrespective of which transmitting means is eifective, means ateach station for always marking the first impulse of a series transmitted from that station, with a character different from the first impulse transmitted from another station, storing means at each station registering the character of the first impulse of each series of impulses impressed on said line circuit, and means controlled by said storing means for determining the direction oftransmission over said line circuit.

6. In a remote control system for railroads, a plurality of stations connected by a line circuit, means at each station for impressing a series of positive and negative impulses on said line circuit, means at each station determining the polarity of the first impulse of a series transmitted from that static-n, storing means at each station registering the polarity of the first impulse of each series of impulses impressed on said line circuit, and means controlled by said storing means when the first impulse of a series is of one polarity to cause the transmission over said line circuit to bejin one direction but when the first impulse of a series is of the other polarity to cause the transmission over said lin circuit to be in the opposite direction.

7. In aremote control system for railroads,

a plurality of stations connected by a line circuit having a different series of positive and negative impulses impressed thereon, a slow acting relay at each of said stations picked up at the beginning of each series and dropped at the end of that series, a two-position polar relay at each station, means controlled in accordance with the polarity of the first impulse of each is series only during the pick-up period of said slow acting relay at that station at the beginning of that series for distinctively controlling said polar relay to thereby render each station either responsive or unresponsive to the remaining impulses of that series.

8. In a remote control system, a control office, a field station, a line wire and a return line wire extending fromsaid control oifice to. said field station,- a line relay at said control office and at said field station included in series with said line wire, a normally closed impulsing contact included in series with said line wire, a selecting contact at said control oifice'fornormally connecting said line wire to said return line wire,

a selecting contact at said field station for normally connecting said line wire to said return line wire, means at said control office for selectively and reversibly connecting a battery between said line wire and said return line wire when said selecting contact at said control ofiice is picked up, means at said field station for selectively and reversibly connecting a battery between said line wire and said return line wire when said selecting contact at said field station is picked up, means, at said control office for intermittently opening said impulsing contact when either one of said selecting contacts is picked up,

and means selectively responsive to the direction of energization and the alternate de-energization f of said line relays when a selecting contact is picked up and said impulse contact is being opened and closed.

9. In combination with a plurality of switching devices at a field station, a single line circuit con necting the field station with a control oflice, means at the control office for energizing said line circuit with impulses of positive and/or negative characters to, transmit control signals over said line circuit to said devices for effecting the control thereof, means at the field station for energizing said line circuit with impulses of posisaid signals for: selecting the direction of transmission over said line circuit.

10. A centralized railway tramc controlling system of the multiple impulse type for transmitting distinctive electrical impulses over a line circuit connecting tWo spaced stations comprising, a first station, a second station, a line circuit connecting said stations, a series of stepping relays at each station, an impulsing relay at said first station controlled by the series of stepping relays at that station for successively'opcning and closing said line circuit to define impulses of current in said line circuit, a plurality'of control devices at said second station, a polarity determining relay at said second station controlled by the series of stepping relays and said devices at said second station for determining the polarity of each impulse, a neutral relay at each station repeating the impulses on said line circuit irrespective of their polarity for controlling the series of stepping relays at the corresponding station, a plurality of controlledrelays at said first station, a polar relay at said first station responsive to the polarity of each current impulse, and a circuit for each controlled relay controlled by a front contact of one of the stepping relays at said first station and by a contact of said polar relay and in accordance with the position of the corresponding control device.

11. A centralized railway traflic controlling system of the multiple impulse type fortransmitting distinctive electrical impulses over a line circuit connecting 'two spaced stations comprising, a first station, a second station, a line circuit connecting said stations, a series of stepping relays at each station, an impulsing relay at said first station controlled by the series of stepping relays at that station for successively opening and closing said line circuit to define impulses of current in said line circuit, a plurality of control devices at said second station, a polarity determining relay at said second station controlled by the series of stepping relays and. said devices at said second station for determining the polarity of each impulse, means for causing said polarity determining relay to remain in its condition during a particular impulse irrespective of the condition of said stepping relays until said impulsing means has terminated such impulse, a neutral relay at each station repeating the impulses on said line circuit irrespective of their polarity for controlling the series of stepping relays at the corresponding station, a plurality of controlled relays at said first station, a polar relay at said first station responsive to the polarity of each current impulse, and a circuit for each controlled relay controlled by a front contact of one of the stepping relays at said first station and by a contact of said polar relay and in accordance with the position of the corresponding control device.

12. In a remote control system, a control ofiice, a field station, a line circuit connecting said control oifice with said field station, means for inter mittently and distinctively energizing said line circuit from a source of current in said control office to provide a series of distinctive impulses, means for intermittently and distinctively energizing said line circuit from a source of current at said field station to provide an additional series of distinctive impulses, means for distinctively characterizing the first impulse of each series, and means governed by the character of the first impulse of a series to determine the source of current to be used for the succeeding impulses of said series.

13. A'remote control system of the synchronous type for transmitting controls and indications between a control oifice and a field station over the same line circuit comprising, a source of current in the control office and another source of current at the field station for energizing said line circuit, means in the control oifice for intermittently opening and closing said line circuit, a series of stepping relays at the control ofiice and at the field station operated sequentially one at a time in response to the energization and deenergization of said line circuit, means in the control office governed by its stepping relays and at times eflective during each deenergization of the line for determining the condition of energization of said line circuit from the source of current in the control oflice in accordance with the controls to be transmitted, means at the field station governed by its stepping relays and efiective at other times during each deenergization of the line circuit to determine the next succeeding condition of energization of said line circuit from the source of current at the field station, and means in the control office and at the field station responsive to the condition of energization of said line circuit at the other end for registering indications and controls respectively.

14. A remote control system of the character described for transmitting indications from a stationto a control office over a line circuit comprising, means at the control office efiective when set into operation to intermittently open and close said line circuit, stepping relays at the control office and at the fieldstation operated sequentially one at a time in response to the energization and deenergization of said line circuit, a battery in the field station, means at the field station controlled by its stepping relays and effective during each deenergization of the line circuit for determining the polarity of the next connection of said battery to said line circuit, means in the control office governed by its stepping relays and responsive to the polarity of energization of said line circuit for eachstep.

15. In a remote control system, a receiver in a control ofiice comprising a line relay, a series of contacts adapted to be closed one at a time in sequence in response to repeated operation of the line relay by a series of impulses of current, means at a field location for imparting a particular character to selected ones of said impulses, a series of indication relays in said control ofiice one for-each impulse, and means for consecutively actuating each of said indication relays, each when one of said contacts becomes closed, to a position in accordance with the character of the next preceding impulse.

16. In a remote control system, a receiver in a control ofiice comprising a line relay, a series of contacts adapted to be closed one at a time in sequence in response to repeated operations of the line relay by a series of impulses of current,

initiated into operation'to transmit a series of distinctive impulses over said line circuit; receiving means at the control office responsive to a series of distinctive impulses on said line circuit transmitted from said field station; receiving means at the field station responsive to a series of distinctive impulses on said line circuit transmitted from said control ofiice; manually controlled initiating means at the control office for initiating the transmitting means at the control ofiice into operation; automatic initiating means at the field station for initiating the transmitting means at the field station into operation; lockout means permitting only one of said transmitting means to be initiated into operation to transmit a series of impulses during any given time and in the event of substantially simultaneous actu ation of said initiating means at the control office and at the field station permitting only said transmitting means at the field station to operate to transmit a series of distinctive impulses; and means allowing said transmitting means at the control ofiice to be initiated into operation by said manually controlled initiating means immediately following any series of impulses irrespective of the presence of another automatic initiation at the field station. n

18. In a remote control system, a circuit having different series of time spaced impulses of distinctive characters impressed thereon, control relay meansincluded in said circuit and operable to distinctive positions to correspond with the distinctive characters of said impulses, a slow acting relay, an energizing cricuit for said slow act .ing relay closed during each impulse on said circuit by said control relay means irrespective of the distinctive character of such impulse so as to cause said slow acting relay to be picked up during the first impulse of any series and to remain picked up until after the last impulse of any series, a storing relay of the polarized electromagnetic stick type, and energizing circuit means for said storing relay energized with one polarity or the other in accordance with the distinctive position assumed by said control relay means only during the pick up periodof said slow acting relay, whereby the character of the first impulse of any series is stored by said storing relay.

19. In a remote control system; a control office and a distant field station; a line circuit connesting the control office and field station to form a normally deenergized closed loop; step-by-step means at the control ofiice and at the field station, each responsive to a series of impulses on' said line circuit to operate through a cycle of operation; sources of current at said control office and at said field station, said sources being of substantially equal potentials; initiating means at the control ofilce for inserting said control ofiice source. in said line circuit to cause its initial energization in a particular direction; initiating means at the field station for inserting said field station source in said line circuit to cause its initial energization in a direction opposite to said particular direction; impulsing means rendered active by the initial energization of said line circuit in either direction to open and close said line circuit to impress a series of time spaced impulses on said line circuit from the particular source then inserted in the line circuit; trans determine the polarity of each successive impulse of the ensuing series in accordance with messages to be transmitted; and receiving means at the control office and at the field station, each being responsive on the successive steps of its step-bystep means only when its transmitting means is ineffective ,to determine the polarity of the impulses for such steps; whereby the simultaneous insertionof both said sources intov said line circuit by said control oflice and field station initiating means fails to energize the line circuit and thereby fails to render active said impulsing means. 7

20. In a normally-at-rest remote control system; a control ofiice and a field station; a line circuit connecting said control ofiice With said field station and comprising a normally closed eenergized loop; a source of current at the control ofiice and another source of current at the field station; field station initiating means for at times inserting the source of current at said field station into said loop circuit to efiect its initial energization; control ofiice initiating means for at other times inserting said source at the control office into said loop circuit to effect its initial energization; means at the control ofiice responsive to the initial energization of said line circuit for intermittently opening and closing said loop circuit so as to cause said line Wires to be energized by time spaced impulses irrespective of "the particular one of said sources inserted in 'saidloop circuit; step-bystep means in the control office and at the field station operated step-by-step in synchronisrn in response to the energization and deenergization of said line wires; indication transmitting means at thefield station controlled byits step-by-step means during each deenergization of said line wires to determine the polarity of the-next succeeding energization of said line wires from said source at said field, station when said field station initiating means has inserted such source into said loop circuit; means at the control ofiice governed by its step-by-step means and responsive to the polarity of energization' of said line wires after each step when said field station indication transmitting means is operating; controlled by its step-by-step means during each deenergization of said line wires to determine the polarity of the next succeeding energization of said line wires from its said source when said control oifice initiating means has inserted such source into said loop circuit; and means at the field station governed by its step-by-step means and responsive to the polarity of theaenergiza tion of said line Wires after each step when said control transmitting means is operating.

21. In a remote control system; a line circuit connecting a control office and a field station to form a normally deenergized closed conducting'loop; step-by-step means at the control of fice and at the field station, each responsive to a series of impulses on said line circuit to op crate step-byestep through a cycle of operation; a source of current at the control office and another source at said field station, said sources being of substantially equal potentials; manuallycontrolled initiating means at the control 'office for inserting said control o-fiice source into said line circuit to cause its initial energization in a particular direction; automatic initiating means responsive to a change in the condition of any one of a plurality of devices at the field station for inserting said field station source into said line circuit to cause its initial energization in a direction opposite to said particular direction; impulsing means rendered active by the initial energization of said line circuit in either direction to open and close the line circuit to impress a series of time-spaced impulses on such line circuit; transmitting means at the control ofiice and at the field station each being efiective on the successive steps of its said step-by-step means only when its source is inserted in said line circuit to determine the polarity of each successive impulse of the ensuing series in accordance with messages to be transmitted; receiving means at the control office and at the field station, each being responsive on the successive steps of its step-by-step means to the polarity of the impulses for such steps only when its transmitting means is inefiective to determine the polarity of the impulses for such steps; and manually operable means for controlling said initiating means at the control office to cause the insertion of said control ofi'ice source into said line circuit in a direction opposite to said particular direction; whereby the operation of said manually operable means upon the simultaneous insertion of both said sources irito said line circuit by the simultaneous operation of said control office and said field station initiating means causes said impulsing means to be initiated into operation and renders the transmitting means at the field station effective by reason of the energization of the line circuit being in the same direction as the energization automatically caused by the initiating means at the'field station.

22. In a remote control system; a single line circuit forming a normally closed deenergized conducting loop arranged to connect a control office and a field station; step-by-step means at the control ofiice and at the field station operated step-by-step in response to a series of impulses on said line circuit; a source of current at the control oifice and another source at the field station, said sources being of substantial equal potentials; manually controlled-initiating means at the control ofiice for inserting said control ofiice source into said line circuit to cause its initial energization in a particular direction; automatic initiating means at the field station for inserting said field station source in'said line circuit to cause its initial energization in a direction opposite to said particular direction; impulsing means rendered active by the initial energization of said line circuit in either direction to open and close saidline circuit to impress a series of time-spaced impulses on said line circuit; cycle demarking means at the control omce and at the field station rendered active in response to the initial energization of said line circuit so as to simultaneously mark the beginning of such series of impulses at the control ofiice and at the field station at substantially the same time, but arranged to mark the end of such series at the control ofiice and at the field station successively in that order, said cycle demarking means at the control ofiice and at the field station respectively controlling their initiating means so as to allow the respective initiating means to become effective only when such cycle demarking means is inactive; transmitting means at the control ofiice and at the field station each being effective onthe successive steps of the step-by-step means only when its source is inserted in said line circuit to determine the polarity of each successive impulse of the following series of impulses in accordance with messages to be transmitted; receiving means at the control ofiice and at the field station each being responsive to the polarity of the impulses on the line circuit on the successive steps of its stepby-step means only when its transmitting means is ineffective during such steps; and manually operable means for controlling the initiating means at the control office to cause the insertion of said control ofiice source into said line circuit to cause its initial energization in a direction opposite to said particular direction to thereby effect the initiation of the system into operation for transmissionfrom the field station to the control office; whereby messages are transmitted from the field station tothe control office during one cycle of operation upon the simultaneous operation of the initiating means at the control ofiice and at the field station with the system being available for a cycle of operation for the transmission of messages from the control oifice to the field station on the next following cycle of operation although the initiating means at the field station is automatically operated to initiate another cycle of operation for the transmission of messages from the field station to the control ofiice by reason of said control ofiice and said field station initiating means becoming successively effective upon the return of-said cycle demarking means to inactive conditions.

23. In a remote control system, a plurality of locations including a control office and a field station, two line wires extending between said control oifice and said field station, sources of electrical energy located at 'said control office and at said field station, means at said control ofiice and at said field station for normally connecting said two line wires in a deenergized loop circuit, means at said control ofiice and other means at said field station, each means for connecting the source at the corresponding location into said loop circuit, selective means determining which source shall be connected into said loop circuit at any one time, means in said loop circuit at said control office for opening and closing said loop circuit at time spaced intervals when a source is included therein to cause its.

energization, step-by-step means at said control oflice and at said field station responsive to take one step for each energization of said loop circuit; means at each location controlled by the step-by-step means at its location when that one of said locations has its source included in said loop circuit as determined by said selective means, to be rendered effective during each deenergization of said loop circuit to determine the polarity with which the source at such location is connected. in said loop circuit; and means at each location controlled by the step-by-step means at its location when the other of said'locations is determining the polarities of the energizations of said loop circuit.

24. In a remote control system of the selector type; the combination with a control omce and a field station, each having a source of current; of a single line circuit connecting said control ofiice with said field station; step-by-step nieans at said control office and at said field station responsive to series of impulses on said line circuit to operate through cycles of operation irrespective of their character; selecting means for energ'izing said line circuit from the source at said control office or from the source at said field station, said selecting means energizing saidline circuit from only one of the sources during any given cycle of operation; impulsing means at said control oflice alone for opening and closing said line circuit at time spaced intervals, whereby a plurality of impulses are placed on said line circuit to cause a cycle of operation of said step-bystep means; and code sending means at said control ofiice and at said field station controlled through contacts of their respective step-by-step means for determining the polarity of the impulse for each step, said code sending means at said control ofiice or at said field station being chosen by said selecting means for any given cycle of operation, whereby messages are transmitted to and from said field station and said control oifice during separate cycles of operation, and whereby the time spacing of said messages is determined wholly in said control office.

25. In a normally-at-rest remote control system, a control ofiice and a field station connected by two line wires forming a normally deenergized loop circuit, a source of current at the field station, means at the field station for initiating the system into operation by inserting said source into said loop circuit to effect its energization, means in the control office for intermittently opening said loop circuit so that said line wires are energized by time spaced impulses from said source, step-by-step means in the control office and at the field station operating step-by-step in response to the energization and deenergization of said line wires, means at the field station controlled by its step-by-step means and effective during each deenergization of said line wires to determine the distinctive character of the next succeeding energization of said line wires from said source, and means in the control ofiice governed by its step-by-step means for responding to the distinctive character of the energization of said line wires after each step.

' NEIL D. PRESTON. 

